Hi
Can anyone confirm the thread type found on K series bsa oil tanks
Was the thread changed at anytime in production ?
I ask as recently I got a screw on alloy cap for a friend - when we managed to find a tank / it also had a cap fitted but had a different thread type
Am just wondering now whether the oil tank cap obtained earlier is in fact a bsa type
It’s a domed alloy cap & a coarser thread than that found in the tank - it has that pie crust outer edge too

Any theories ?

Br
Job

email (option): Jonnyob1atgooglemail.com

John the K and W series C models have those pie crust caps for the oil and petrol. But I've noticed that the earlier 30's bikes had caps with a different thread and more finger indents to the pie crust. Ron

email (option): ronpier@talk21.com

You have e mail John...Ian

These are John's caps. He may have to explain what's what !

There are 2 caps involved
One is marked oil
The other has no markings but does have a small breather hole

The 3rd cap seen is one which came with a tank bought at cheddar
When we checked we found that the 2 other caps did not fit the tank - thread was different - but I also note the pie crust surround had 8 indentations on its outer

I think Ron nailed it with his photo / they are perhaps from a bsa 250 K or W

It was on my mind as to what they might have been fitted to

Thanks to Ron, Ian & Rik for their help
Br
Jo’b

email (option): Jonnyob1atgooglemail.com

Looking in the 1939 civilian spares list, the C10s had Petrol tank filler cap 29-7790(2), so two identical caps with no mention of "Oil"? Looks like 8 notches around the edge.

The book gives the part number for the M20 oil tank cap as 66-8317 with many notches around the edge, 66 part numbers are a generation on from 29 so perhaps thats the difference in thread?

Rob

This changed for the 1940 season Rob. Where the extended oil return pipe required some room inside the cap.29-7791. The petrol cap 29-7790 retained the dome baffle. John let me know if those two caps are for sale. Cheers Ron

email (option): ronpier@talk21.com